Dealkylation of aromatic hydrocarbons



United States Patent (3 i DEALKYLATION or AROMATIC HYDROCARBONS Harry Ciouglr, Norton-on-Tees, England, assignor to Imperial Chemical Industries Limited, a corporation of Great Britain N Drawing. Application June 29, 1951, Serial No. 234,435

Claims priority, application Great Britain July 17, 1950 4 Claims. (Cl. 260-672) This invention relates to the dealkylation of aromatic hydrocarbons.

Hitherto the more valuable aromatic hydrocarbons, such as benzene, toluene and the xylenes, have usually been obtained from oils recovered during the gasification and coking of coal, from coal tars, from fractions of certain petroleums, and from petrols obtained by the treatment of petroleum or its fractions, the individual aromatic hydrocarbons being obtained from such sources for example by fractional distillation, solvent extraction or a combination of such processes. Often such materials from which the individual aromatic hydrocarbons are to be isolated do not contain a high proportion of the more valuable lower aromatic hydrocarbons. Furthermore, they are often contaminated with sulphur compounds which tend to appear in the isolated aromatic hydrocarbons, rendering the latter unsuitable or unsatisfactory for many purposes; thus even when the aromatic hydrocarbons are isolated they often require further treatment to remove the undesired sulphur compounds from them.

An object of the present invention is to provide a process whereby materials containing monocyclic aromatic hydrocarbons are treated to increase their proportion of valuable lower aromatic hydrocarbons while decreasing the proportion of sulphur compounds which may be present, or substantially removing these sulphur compounds, whereby an enhanced source of individual lower aromatic hydrocarbons of improved purity is obtained. A further object is to provide a process for the treatment of individual aromatic hydrocarbons such as toluene or a xylene to produce lower aromatic hydrocarbons. A particular object of the present invention is to produce enhanced quantities of high grade benzene, toluene and xylenes from materials containing or consisting of higher aromatic hydrocarbons.

In its broader aspects the process of the present invention comprises the dealkylation of aromatic hydrocarbons.

According to the present invention, therefore, there is provided a process for the dealkylation of monocyclic aromatic hydrocarbons which comprises treating a monocyclic aromatic hydrocarbon at a temperature above 5 00 'C. and at a pressure higher than 100 atmospheres gauge with hydrogen in the presence of a catalyst comprising an aluminium silicate and ferric fluoride.

While in general the alkyl groups to be removed may contain several carbon atoms, for example ethyl and propyl groups, we have found the process of the present invention particularly suitable for the removal of methyl groups. Particularly satisfactory results have been ob tained, for example, in the dealkylation of toluene, xylenes, ethyl benzene and trimethylbenzenes. Furthermore, the process is suitable for the treatment of hydrocarbon mixtures containing monocyclic aromatic hydrocarbons, examples of such mixtures being products obtained by extracting petroleum products such as petrol and kerosene with liquid sulphur dioxide, oils, for ex- 2,709,193 Patented May 24, 1955 ample petrols obtained by the conversion of petroleum and its fractions, and oils recovered during the gasification and coking of coal and extracts or fractions from the distillation of coal tar. In addition to paraflins and naphthenes, the hydrocarbon mixtures may also contain olefines and diolefines. Good results have been obtained with fractions of cracked petrols boiling within the range C. to C. and in the range 150 C. to C. When treating fractions of cracked petrols results indicate that in addition to dealkylation, some dehydrogenation and cyclization may have occurred, leading to the formation of further aromatic hydrocarbons. In this specification the word conversion as applied to petroleum and its fractions is intended to mean those processes by which petroleum and its fractions are treated to obtain petrols, naphthas, kerosenes, and other valuable products, the processes including cracking and catalytic treatments-to cause dehydrogenation and isomerization.

Catalysts suitable for use according to the present invention may contain a variety of aluminium silicates, which may be synthetic or naturally occurring silicates such as the so called earths. Particularly satisfactory results have been obtained with the use of a catalyst comprising the earth sold under the trade name Super filtrol. The ferric fluoride may be introduced into the catalyst in a variety of ways, for example ferric hydroxide may be dissolved in an excess of aqueous hydrogen fluoride which is then used to make a paste of an aluminate silicate, the paste then being extruded and dried at a temperature in the range 150 C. to C. If desired the above mentioned paste may be dried, ground to a powder, formed into granules and then extruded. Alternatively, iron sesquioxide, ferric hydroxide'or ferric nitrate may be mixed with an earth which has been treated with hydrogen fluoride, the mixture then being calcined, or the earth may be made into a paste with iron sesquioxide and the mixture treated with hydrogen fluoride, followed by extrusion and drying at 150 C. to 180 C.

A wide range of temperatures above 500 C. may be used. At temperatures below 500 C., saturation of aromatic hydrocarbons tends to occur and this tendency increases as the temperature is decreased below 500 C. Furthermore, at temperatures below 500 C., there is a tendency to disproportionation of alkyl groups leading to the formation of undesired aromatic hydrocarbons of higher molecular weight. As the temperature is increased there is a tendency for cracking reactions to occur accompanied by polymerization of the cracked products and for this reason it is preferable to operate the process of the present invention in the temperature range 500 C. to 600 C. More preferably the process is operated at temperatures in the range 540 C. to 570 C.

The pressure used in the process of the present invention will depend in general on the type of aromatic hydrocarbons desired. It is desirable however, to avoid using pressures lower than 100 atmospheres gauge as there may be a tendency to disproportionation. We have found that pressures in the range 200 to 300 atmospheres gauge give particularly satisfactory results. As the pressure is increased it is desirable to increase the temperature of operation, to avoid saturation of the aromatic hydrocarbons. In general, in commencing operation of the process, the desired pressure will be attained by the introduction of substantially pure hydrogen into the apparatus, and it will thereafter be maintained by the introduction of similar gas as required.

an autoclave and keeping them; there until reaction'has proceeded to a satisfactory extent, it is preferable to rial, maintained at a suitable temperature.

carry it out in a continuous process, that is in one in which the reactants are passed over the catalytic mate- It has been found that in such a continuous process the rate of passage of the reactants over the catalyst has an important eilect on the composition of the product, as will be evident from the record given hereinafter, of experiments carried out according to the invention.

As the process of the present invention in general is accompanied by the formation of varying amounts of carbonaceous material, it may be desirable from time to time to regenerate the catalyst for example by the passage thereover of an oxygen-containing gas such as air and/or steam while maintaining the catalyst at elevated temperature. for example at intervals of 300 hours when working a continuous process.

In addition to enhancing the content of lower monocyclic aromatic hydrocarbons in a given starting material when operating according to the present invention, the additional advantage is obtained that the proportion of deleterious sulphur compounds contained in the starting material is considerably decreased. For example, from starting materials containing 0.5% to 1.0% of sulphur compounds (expressed as elementary sulphur), there may be obtained products containing 0.005% and lower of such compounds.

It will be understood that the products obtained from the operation of the process may be treated by any con venient means for the isolation of the individual monocyclic aromatic hydrocarbons, for example, simple fractional distillation, azeotropic distillation, and crystallization, or a combination of such methods may be used.

Example 1 This regeneration step may be carried out,

Experiments were carried out in which a mixture of xylenes, together with hydrogen was passed over a catalyst prepared as hereinafter described and comprising Superfiltrol" and ferric fluoride, the pressure being maintained at 260 atmospheres gauge, various temperatures being used. The proportion of hydrogen to xylenes was 1000 liters of hydrogen per liter of liquid xylenes. The rate of feeding the mixture of xylenes was 1.5 liters of liquid xylenes per liter of catalyst per hour, the results being as follows:

Percentage by weight in the product Temperature saturated Benzene Toluene cyllallgggqtllb- Nil 9-10 9-10 a4 23 23 12 10-12 35-40 4042 Nil Nil Example 2 The effect of varying the rate of feeding the mixture of xylenes, using the same kind of catalyst as in the above described experiments and in the presence of hydrogen, while maintaining the temperature at 550 C.

Percentage by weight,

Feed rate: liters of xylene per liter of catalyst in the products of per hour Benzene Toluene Example 3 Using the same catalyst, a temperature of 550 C. and a pressure of 260 atmospheres gauge and operating in the presence or" hydrogen with various rates of feeding trimethylbenzenes, the following results were obtained.

The above results in Examples 2 and 3 show that with increasing feed rate, the production of the lower aromatic hydrocarbons tends to decrease and that there is a decrease in the readiness with which the alkyl groups are removed from the lower alkylated aromatic hydrocarbons.

Example 4 A fraction of cracked petrol having a boiling range between C. and C. and containing 37% by weight of aromatic hydrocarbons was passed together with hydrogen over a catalyst prepared as above described, the catalyst being maintained at 550 C. and the pressure at 250 atmospheres gauge. The aromatic content of the cracked petrol cut was predominantly trirnethyl benzenes; there was no benzene, toluene or xylenes in the fraction. The rate of feeding the cracked petrol cut was 1 liter per liter of catalyst space per hour, and the ratio of hydrogen to cracked petrol cut was 1000 liters per liter of liquid. The product contained 48% by weight of benzene and 25% by weight of toluene.

Example 5 A coke oven benzole was treated under the conditions mentioned in Example 4 except that the feed of liquid was 1 liter of benzole per liter of catalyst space per hour, and the ratio of hydrogen to benzole was 900 liters per liter of liquid. The sulphur compounds in the feed were equivalent to 0.60% of elementary sulphur, while in the product these were decreased to 0.003% by weight. Analysis of the product showed that compared with the feed material there had been an increase in the benzene content.

Example 6 Substantially pure toluene was treated under the same conditions as described in Example 5, when it was found that the product contained 47% by weight of benzene.

Example 7 The following record of experiments using xylenes as feed material show the efiect of operating with increasing pressures:

Pressure, atmospheres 150 200 225 250 Feed rate: 1t./1t;. catalyst spacelhoun. 1 1 1 I 1 Lt. Gas/1t. Xylenes 980 990 1,030 I 900 Temperature, C 550 550 550 550 Product Recovery, Wt. Percent 92.8 87. 89. 4 81.7 Product Composition:

Percent Light Ends 4. l 3. 0 3. 0 5. 0 Benzene 7. 5 12.0 13. 5 16. 5 Toluene 36,0 1 39.5 40.5 42.0

I claim:

1. A process for the dealkylation of monocyclic aromatic hydrocarbons containing at least one substituent alkyl group which comprises the step of treating with hydrogen a monocyclic aromatic hydrocarbon containing at least one substituent alkyl group at a temperature above 500 C. and a pressure higher than 100 atmospheres gauge in the presence of a catalyst consisting essentially of aluminum silicate and ferric fluoride.

2. A process as recited in claim 1 in which the temperature employed is in the range of from 500 C. to 600 C. and the pressure employed is in the range of from 200 to 300 atmospheres gauge.

References Cited in the file of this patent UNITED STATES PATENTS 2,341,782 Ipatieff et al. Feb. 15, 1944 2,382,505 Schulze Aug. 14, 1945 2,413,868 Frey Jan. 7, 1947 2,425,559 Passino et a1. Aug. 12, 1947 2,436,698 Oblad Feb. 24, 1948 2,438,570 Mattox Mar. 30, 1948 2,527,529 Cade Oct. 31, 1950 FOREIGN PATENTS 637,595 Great Britain May 24, 1950 OTHER REFERENCES Thorpe: Dictionary of Applied Chemistry, vol. 1, page 560 (1 page), pub. by Longmans, Green and C0., New York (1921). 

1. A PROCESS FOR THE DEALKYLATION OF MONOCYCLIC AROMATIC HYDROCARBONS CONTAINING AT LEAST ONE SUBSTITUENT ALKYL GROUP WHICH COMPRISES THE STEP OF TREATING WITH HYDROGEN A MONOCYCLIC AROMATIC HYDROCARBON CONTAINING AT LEAST ONE SUBSTITUENT ALKYL GROUP AT A TEMPERATURE ABOVE 500* C. AND A PRESSURE HIGHER THAN 100 ATMOSPHERES GUAGE IN THE PRESENCE OF A CATALYST CONSISTING ESSENTIALLY OF ALUMINUM SILICATE AND FERRIC FLUORIDE. 